how-to-do-x's Introduction

I want to do "X"

The following is a guide for how to get started with programming side projects. If something's missing and you know about it, feel free to submit a pull request and add it.

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Building Programming Languages

Overview

Building languages is not as hard as it may appear! In general, the key concepts are:

Grammars, or the formal structure of a language.
Lexing, or the conversion of text into abstract "tokens" that can be used in the grammar. For example, most languages convert the + into a PLUS token.
Parsing, or the conversion of "tokens" (pieces of a language) into an Abstract Syntax Tree.

First Steps

A good first project is to build a calculator that can compute things like this:

1 + 2 * 5

Step 1: Write a grammar

You should probably write this in EBNF form. It doesn't need to have the exact same syntax, but it's useful to understand the conventions.

To get you started, here's a partial grammar for the calculator:

add: add '+' add | NUM.
NUM: [0-9].

Notice that grammars are written as recursive "rules". In the example above, the string 1 + 2 would enter the add rule, then recurse till it matched the NUM.